Grading machine



Mach so, 1937.

H. P. DAWRS El AL GRADING MACHINE Filed Aug. 25, 1932 2 Sheets-Sheet l [I 7 4 I' I: 3 6 9 1 J 1 L I 5 20 ATTORNEY March 30,1937. H. D HAL v 2,075,097

' GRADING MACHINE Filed Aug. 25, 1952 2 Sheets-Sheet 2 INVENTORS HARVEY P. DAwzs HENRY z Fowslz. BY

A TTORNEY Patented Mar. 30, 1937 UNITED STATES PATENT OFFICE GRADING MACHINE Application August 25, 1932, Serial No. 630,346

6 Claims.

This invention relates to a machine for grading granular materials and other finely divided solid materials. An object of the invention is to provide a grading machine which is adapted to the accurate mechanical separation of granular material into a plurality of components according to particle size.

In the course of separation of crushed granular material at the place of manufacture, it is customary to use a series of inclined screens arranged in vertical relationship and to reciprocate them back and forthwhile the material to be graded falls on the uppermost screen from some source of supply. The particles that are too coarse to pass through the uppermost screen move down to the lower end of this screen and thence into a container. The grits which pass through the uppermost screen fall on a finer screen below, where the separating process described above is repeated. The number of screens used one above another in this manner depends on the degree of classification of grain sizes desired.

The separation of grain obtained in the manner just described is subject to difiiculties arising, for example, from the fact that some grain may pass down an inclined screen to the discharge at the lower end without reaching the meshes of the screen; hence, the separated portions are mixtures of grits of various sizes and are not as ao- 50 curately separated as is desired for many pur-- poses.

It is evident that it is desirable to have a grading apparatus capable of giving more accurate grading than is ordinarily obtainable in grading 35 commercially. When more accurate grading apparatus is available, it is possible to compare the performance of various separating devices used in commerce and to take measures to correct faulty separating apparatus.

40 The new grading machine which permits more accurate mechanical analysis of grain samples is illustrated by the accompanying drawings in Figure 7 shows a vertical section of a modified screen which is supported on roller or ball bearings; and

Figure 8 is a fragmentary section on the line VIII-VIII of Figure 7. 5

Referring to the drawings in detail, a cradle 2 which supports a plurality of trays 3 is mounted for reciprocation in guides 4 which are supported on a base 5. The cradle 2 is rigidly connected with four bars 6 whose axes lie approximately in 10 the median plane of the cradle. These-bars 6 are reciprocated in the guides 4 with the aid of a pitman I, one end of which is mounted to oscillate abouta horizontal axis fixed in the median plane of the cradle. The opposite end of the pit- 15 man is formed into a sleeve 8 which oscillates about a member 9 which is eccentrically mounted with respect to the axis of rotation of a motor ll.

Each tray is provided with a plurality of ledges l2 which have horizontally disposed smooth sur- 20 faces on which screens l3 can slide. The lower surfaces of the frame of the screen are also. 7 smooth. Projections ID are provided against which the sliding screens l3 bump during the operation of the grading mechanism. These pro- 25 jections Ill are adjustable in a horizontal plane to and from their supports for the purpose of varying the length of glide of the screen. In order that this bumping action may have about the same force for either direction of motion of the cradle, it is necessary to level the base 5 carefully and to have the guide openings for the rods 6 so positioned that the cradle is reciprocated in a horizontal direction.

The screens I3 are graduated in mesh size, the top screen having the coarsest mesh and each of the lower screens a finer mesh than the one immediately above it. The material that passes through each screen falls into a funnel I4 from which it is discharged through an outlet IS. The 40 material which is thus discharged falls on the next lower screen except in the base of the lowest orifice l5 which discharges into a container 20. After the cradle has been reciprocated for a suificient length of time to pass substantially all the materialthat can go through the screens, the contents of each screen and of the container are weighed and compared with the mass of the sample which was supplied to the uppermost screen. The percentages for each component obtained by the mechanical analysis can then be calculated.

The rate of reciprocation which gives the most effective screening varies with the average size of the granules and varies also with the character of the granular material. For example, a grading test on fine silicon carbide, about 220 grit, showed that 336 reciprocations of the screen per minute were more effective than 268 reciprocations per minute. On the other hand, in the case of coarse silicon carbide, about 24 grit, 260 reciprocations per minute were found to be more effective than 331 revolutions per minute.

In the case of quartz, a higher speed is found necessary to shake it through a screen than is the case with most common abrasives.

For thorough screening, it is found desirable to make the frame of each screen l3 light in weight in order that they may freely slide upon the ways or ledges l2. The frames transmit to the screens and their contents minute vibrations which aid in the screening action. Screen frames made of wood or of phenol condensation product resin cured to the C stage (known to the trade as bakelite) have been found to give good screening effects, but heavy metal frames damp the vibrations produced by the bumping of the frame against the projections III in such a manner that the grading is very imperfect.

In the case of the modified screen shown in Figures 7 and 8, the frame l3" of the screen is mounted on a plurality of balls or rollers l8 which roll in grooved slots IS. The latter are of sufficient length to permit the screen to glide freely between the opposite end projections l0. In this case the retardation of the motion of the screen relatively to its support because of friction is minimized so that the granular material on the screen fabric is more thoroughly jarred by the impacts of the screen against the projections Ill than is the case where there is much frictional resistance to the gliding of the screen.

The funnels H are made of resilient metal having smooth upper surfaces so that the grain which .fails from the screen will move easily down to the orifice i5. Copper, tin plate and galvanized iron have-been found to be satisfactory for this purpose, whereas aluminum and lead retard the movement of the granular material in the fine grit sizes.

One method of fastening the fabric Ii of the screen in its holder is illustrated in Figures 5 and 6. The lower part of the holder has a deep groove 2| in a recessed portion of the holder. The fabric I6 is put down with its edges extending over the groove 2| and a cord i1 is laid down on the fabric and over the groove. The cord I I is then pressed in contact with the fabric into the groove. This procedure holds the fabric taut in the holder.'

While reference has been made by way of 55 example to the grading of abrasive grain, our

grading machine may be used with advantage in the classification of other granular materials not usually considered abrasive.

We claim:

1.. A screen for the separation of granular material comprising a frame having light sides and ends and a relatively larger base, a groove in said base, means for locking fabric in said frame comprising a cord which retains the outer portions of said fabric in said groove, and bumpers on the ends of said frame for distributing jars to the material being separated by the screen.

2. Apparatus for grading granular material comprising a base provided with four standards each having a bearing disposed horizontally at the same height, a cradle'having four projecting supporting rods adapted to be reciprocated in said bearings, a plurality of trays mounted in said cradle symmetrically above and below the hori- 7 zontal plane containing the axes 9: sa d b l 'ings, 7

each of said trays having a plurality of smooth.

screen supporting surfaces of similar height, a light screen mounted for sliding motion on said last mentioned surfaces in each tray. and a funnel disposed in each of said trays below the screen' and having an outlet under the central portion of each screen.

3. Apparatus for grading granular material comprising a cradle mounted for horizontal reciprocation in bearings whose axes are disposed in the median plane of the cradle,a plurality of I trays mounted in said cradle symmetrically above ent metal mounted in each tray below each screen,

said funnel having a small outlet under the central portion of the screen.

4. A grading machine for the rapid separation I of small samples of granular material into a plurality of sizes, said machine'comprising a cradle mounted for reciprocation in a horizontal direc tion with respect to a stationary base, a plurality of parallel sliding. bars rigidly attached to said cradle and extending from opposite sides thereof,

guiding and supporting members for said sliding bars, said members being mounted on said base rocatory movement of said sliding bars, a plurality of screens mounted in superimposed relationship within said cradle for limited horizontal movements parallel to the direction of reciprocation of and having bearing surfaces for horizontal recipthe cradle, opposite end stops for each screen mounted on the frame of said cradle, the center line of theopposite end stops for a given screen being parallel to the direction of reciprocation of the cradle and the distance between said opposite end stops being manually adjustable, and means for reciprocating said cradle in a horizontal direction.

5. Apparatus for the rapid mechanical analysis of small samples of granular material, said apparatus comprising four vertically disposed standards mounted in rectangular arrangement on a heavy base, a cradle having four vertically disposed standards mounted in rectangular arrangement in the space between the base standards by means of four parallel supporting members each adapted to be reciprocated in a horizontally disposed bearing in an adjacent base standard, a plurality of trays mounted symmetrically above and below the median horizontal plane of said cradle, a screen mounted for limited horizontal oscillation with respect to each tray and on a plurality of smooth supporting surfaces arranged on opposite sides of the tray to permit oscillation of the screen with equal facility in opposite directions on the tray, a funnel disposed under eachscreen and having a small opening vertically over the mean position of the center of the screen or vessel into which said funnel discharges, and means for rapidly reciprocating the cradle to separate the granular material into a plurality of sizes.

6. Apparatus for the rapid mechanical analysis of small samples of granular material, said apparatus comprising four vertically disposed standards mounted'in rectangular arrangement on a heavy base, a cradle having four vertically disposed standards mounted in rectangular arrangement in the spaccbetween the base standards by means of four parallel supporting members each adapted to be reciprocated in a horizontally disposed bearing in an adjacent base standard, a plurality of trays mounted symmetrically above and below the median horizontal plane of said cradle, a screen mounted for limited horizontal oscillation on smooth supporting surfaces on each tray, a projection on one or more of the trays arranged in the line of motion of the supported screen to give intermittent jars thereto, a metal 10 funnel having a smooth upper surface disposed under each screen and having a small opening vertically over the center of the screen or vessel into which it discharges, and means for rapidly reciprocating the cradle to separate the granular material into a plurality of sizes remaining on the screens, as well asinto material which passes through all the screens. 

